The Fenton and photo-Fenton mediated degradation process of Orange II was investigated in a flow photo-reactor. The degradation was monitored as a function of the wavelength of the applied light, recirculation flow rate, amount of H2O2 and the initial concentration of Orange II. Optimization of the photo-Fenton degradation mediated by Fe-Nafion membranes indicated that an Orange II (0.25 M) solution discolored above 95% within 2.5 hours at an H2O2/Orange II ratio of 20. A concomitant mineralization of 40% of Orange II was observed after 5 h reaction. Homogeneous photo-Fenton processes were able to fully discolore Orange II within 1 hour and concomitantly fully mineralize the dye in the presence of Fe(III) (2 ppm) and an H2O2/Orange II ratio of 20. Surfactants such as linear alkylbenzene sulphonates (LAS) and K-perfluoroalkyl sulphonate (FT 800) slowed down the Orange II abatement in photo-Fenton processes.